近日,，武漢植物園成功測定了孑遺蕨類植物桫欏的葉綠體基因組全序列，并對其進行了進化基因組學分析,。研究發(fā)現(xiàn)桫欏的葉綠體組全長為156,661堿基對,，共編碼117個基因，其中蛋白基因85個,、tRNA基因28個以及rRNA基因4個,。在基因內(nèi)容上，所含的trnR-UCG基因目前僅在桫欏中被報道,，它極有可能代表的是樹蕨類的獨有特征,。基因順序方面,，在trnD-GUC基因處,，鑒定出蕨類植物曾經(jīng)歷的一個新倒位。另外,，桫欏葉綠體基因組還存在一長度為565堿基對的特殊區(qū)域,，它位于一古老倒位的末端，內(nèi)含11個串聯(lián)重復(fù),。
這些結(jié)果不僅為認識葉綠體基因組的結(jié)構(gòu)和組織方式提供了新的啟示,，而且為后續(xù)的蕨類植物系統(tǒng)發(fā)育基因組學和分子適應(yīng)性進化研究奠定了堅實基礎(chǔ)，具有重要的里程碑意義,。
該研究是由中國科學院武漢植物園博士研究生高磊等人在中國科學院“百人計劃”王艇研究員指導(dǎo)下完成的,，中山大學作為合作單位參與了部分工作。此研究成果6月11日發(fā)表在國際重要學術(shù)期刊BMC Evolutionary Biology上,。（生物谷Bioon.com）
生物谷推薦原始出處：
BMC Evolutionary Biology 2009, 9:130doi:10.1186/1471-2148-9-130
Complete chloroplast genome sequence of a tree fern Alsophila spinulosa: insights into evolutionary changes in fern chloroplast genomes
Lei Gao1,2 , Xuan Yi1,2 , Yong-Xia Yang1,2 , Ying-Juan Su3 and Ting Wang1
1Wuhan Botanical Garden, Chinese Academy of Sciences, Wuhan, Hubei 430074, PR China
2Graduate School, Chinese Academy of Sciences, Beijing 100039, PR China
3State Key Laboratory of Biocontrol, School of Life Sciences, Sun Yat-sen University, Guangzhou, 510275, PR China
Background
Ferns have generally been neglected in studies of chloroplast genomics. Before this study, only one polypod and two basal ferns had their complete chloroplast (cp) genome reported. Tree ferns represent an ancient fern lineage that first occurred in the Late Triassic. In recent phylogenetic analyses, tree ferns were shown to be the sister group of polypods, the most diverse group of living ferns. Availability of cp genome sequence from a tree fern will facilitate interpretation of the evolutionary changes of fern cp genomes. Here we have sequenced the complete cp genome of a scaly tree fern Alsophila spinulosa (Cyatheaceae).
Results
The Alsophila cp genome is 156,661 base pairs (bp) in size, and has a typical quadripartite structure with the large (LSC, 86,308 bp) and small single copy (SSC, 21,623 bp) regions separated by two copies of an inverted repeat (IRs, 24,365 bp each). This genome contains 117 different genes encoding 85 proteins, 4 rRNAs and 28 tRNAs. Pseudogenes of ycf66 and trnT-UGU are also detected in this genome. A unique trnR-UCG gene (derived from trnR-CCG) is found between rbcL and accD. The Alsophila cp genome shares some unusual characteristics with the previously sequenced cp genome of the polypod fern Adiantum capillus-veneris, including the absence of 5 tRNA genes that exist in most other cp genomes. The genome shows a high degree of synteny with that of Adiantum, but differs considerably from two basal ferns (Angiopteris evecta and Psilotum nudum). At one endpoint of an ancient inversion we detected a highly repeated 565-bp-region that is absent from the Adiantum cp genome. An additional minor inversion of the trnD-GUC, which is possibly shared by all ferns, was identified by comparison between the fern and other land plant cp genomes.
Conclusion
By comparing four fern cp genome sequences it was confirmed that two major rearrangements distinguish higher leptosporangiate ferns from basal fern lineages. The Alsophila cp genome is very similar to that of the polypod fern Adiantum in terms of gene content, gene order and GC content. However, there exist some striking differences between them: the trnR-UCG gene represents a putative molecular apomorphy of tree ferns; and the repeats observed at one inversion endpoint may be a vestige of some unknown rearrangement(s). This work provided fresh insights into the fern cp genome evolution as well as useful data for future phylogenetic studies.
